In one aspect, this invention relates to a method of making supported palladium/silver compositions exhibiting improved acetylene hydrogenation catalyst performance. In another aspect, this invention relates to a process for selectively hydrogenating acetylene to ethylene employing supported palladium/silver catalysts having been prepared by the preparation method of this invention.
The selective hydrogenation of acetylene being present as an impurity in monoolefin-containing streams (e.g., ethylene streams from thermal ethane crackers) is commercially carried out with an alumina-supported palladium/silver catalyst, substantially in accordance with the disclosure in U.S. Pat. No. 4,404,124 and its division, U.S. Pat. No. 4,484,015. The operating temperature for this process is selected such that essentially all acetylene is hydrogenated to ethylene (and thus removed from the feed stream) while only an insignificant amount of ethylene is hydrogenated to ethane (to minimize ethylene losses and to avoid a "runaway" reaction which is difficult to control, as has been pointed out in the above-identified patents). The selective acetylene hydrogenation process can be most effectively controlled when there is a large difference between the temperature at which essentially all acetylene is hydrogenated and a higher temperature at which excessive ethylene-to-ethane conversion occurs. Even though the Pd/Ag/Al.sub.2 O.sub.3 catalyst described in the above-identified patents is an excellent catalyst, the present invention represents an improvement in the preparation of this catalyst and related catalysts and their use for the selective acetylene hydrogenation.